This invention relates to apparatus for measuring injection speed of a plunger of a die cast machine.
Usually, for the purpose of supervising the casting conditions of a die cast machine, the high injection speed at the injection step is measured. According to prior art injection speed measuring apparatus, an average speed is measured or an instantaneous speed at a portion of a high speed section is measured.
More particularly, according to the apparatus for measuring the average speed, an average speed .beta. in a section A is measured as shown in FIG. 1. As a consequence, the measured average speed .beta. is substantially smaller than the highest injection speed .alpha. wanted to know.
In apparatus for measuring an instantaneous speed, positions l.sub.1 and l.sub.2 between which the injection speed reaches a predetermined high speed are set for measuring an average speed in a section between positions l.sub.1 and l.sub.2, as shown in FIG. 2. With this apparatus, however, it is necessary to set the positions l.sub.1 and l.sub.2 in a region in which the injection speed becomes a predetermined high speed. Accordingly, where the injection speed varies as shown in FIGS. 3a and 3b with respect to the direction l of the plunger movement, the measured maximum speed varies greatly as shown by .DELTA.V.sub.1.
According to other injection speed measuring apparatus, the peak value of an analog waveform regarding the injection speed is held so as to measure the peak value thus held. Alternatively, an injection speed waveform is divided into a plurality of sections to obtain average speeds of respective sections so as to measure the highest one.
According to the apparatus for measuring the peak value held, as shown in FIG. 4, for example, when holding the peak value of the analog waveform of the injection speed there is a fear of holding the peak value V.sub.p of the surge component, thus measuring a speed higher than an actual maximum speed V.sub.max.
In apparatus for measuring the average speed in a predetermined section, it is necessary to preset a measuring section in which the injection speed reaches a maximum speed, as shown in FIG. 5. However, when the injection speed characteristic varies as shown by a dotted line curve, the preset measuring section varies, whereby the measured value of the maximum injection speed varies greatly.
In apparatus in which the waveform of the injection speed is divided into a plurality of sections to obtain average speeds i respective sections, a substantially desired maximum injection speed can be obtained as shown in FIG. 6. However, when the peak of the maximum injection speed is pointed as shown in FIG. 7a or rounded as shown in FIG. 7b, even when the maximum speed is the same, the measured speed varies greatly.